Field of the Invention
This invention relates to a method and apparatus for the treatment of polluted gases and liquids.
In order to be able effectively to irradiate with UV light in a continuously operating throughflow reactor highly contaminated waste water having a low light transmission, DE-A-40 05 488 proposes the use of a falling film or flowing film reactor. The falling film reactor consists of a reactor tube in which an UV radiator surrounded by a quartz protective tube is arranged concentrically. The reactor tube has an inlet for the liquid for treatment at the top and an outlet at the bottom. A restrictor at the top end of the reactor tube ensures that the water for treatment flows at a slightly positive pressure through the reactor tube, which is open at the bottom. The water flows in the form of a falling film down the inner walls of the reactor tube. There is no contact between the water and the quartz protective tube. Mass transfer with the surrounding gas takes place at the surface of the film. DE40 05 488 proposes utilising this effect to strip readily volatile substances. A disadvantage of the described reactor is that it is suitable only for the detoxification of drinking water of liquids. The reactor is not considered for use for air purification since the contact times of the air with the falling film would be too short and the mass transfer taking place under these conditions would be inadequate in the light of experience. Accordingly the only consideration has been to utilise the mass transfer from the liquid phase to the gas phase to strip readily volatile substances out of the liquid phase. DE-A-38 37 905 proposes an apparatus for the treatment of liquids and/or gases by means of UV light sources wherein the UV lamps of different emission spectra are used simultaneously. The UV lamps are disposed in or around a tubular reaction chamber. The medium for treatment is passed through the reaction chamber in concurrent or countercurrent flow, depending upon the reaction chamber construction. Although this apparatus may be suitable for the treatment of liquids, its utility for the effective treatment of gases appears doubtful. Many organic compounds, e.g. benzene, toluene, etc., occurring in polluted waste air are admittedly UV-light-absorbent but they are chemically extremely stable so that the most that can partially occur is a breaking up of the molecules during their passage through the reactor. Known methods of treating polluted gases very often therefore make use of a wet stage in order to remove adhering pollutants from the gas. In the wet stage the gas is contacted with a liquid, e.g. in a Raschig column or by means of a spray mist in order to convert the pollutants to the liquid phase. This operation can then be followed by further treatments.